Bags used in automated filling processes have been known for many years. Traditionally, these bags are produced from continuous sheets or rolls of bag material, typically organic or other plastic material. In many manufacturing processes, a sheet of bag material is folded and sealed to form a continuous flat bag "tube" having an upper and a lower layer. This tube may be further folded or pinched to form multiple layers in, for example, side gusseted bags. The tube may then be again sealed, cut, stamped, separated and stacked on storage wickets for subsequent use in the automated bag filling operation. Storage wickets onto which the newly formed bags are stacked are typically U-shaped pieces of thin rigid material, which fit through aligned wicket openings formed in the bags on the stack.
During bag filling, stacks of bags are transferred from the wickets onto mandrels which make up part of a bag filling mechanism. After the wicket is removed, the bags remain aligned and stacked on the mandrels. Typically, caps are then positioned over the exposed end of each filling mandrel thereby holding the stacked bags in formation so that they may be used in the filling operation.
During the bag loading process, suction cups or other grabbing means separate the upper layers of the bag from the lower layer thereby initiating the opening of the bag. A puff of air delivered through needle and check valve arrangements further opens the bag while the lower layer of the bag remains securely positioned on the filling mandrels. As the bag opens, loader arms unfold within the filling edge of the bag which open the bag completely while a filling arm pushes items into the bag and ultimately pushes the filled bag off of the mandrel. Examples of wicketed bags and their filling are disclosed in Altman, Jr., U.S. Pat. No. 3,044,233; Melin, U.S. Pat. No. 3,797,732; Lieberman, U.S. Pat. No. 3,640,450; Lehmacher, U.S. Pat. No. 3,996,524 and Inagaki, U.S. Pat. No. 4,669,251. These patents relate generally to bags having a single solid "bridge" of bag material positioned between the wicket opening and the edge of the bag. This "bridge" must be broken in order to release the bag from the wicket.
While wicketed bags represent a popular choice among manufacturers in automated filling operations, such bags share a number of problems which heretofore have not been satisfactorily addressed. One such problem stems from the difficulties often associated with opening the bags during machine loading. For example, side gusseted bags, bags with side folds, tube-style bags, and other bags having multiple panels extending in length past a wicket opening, are particularly difficult to open fully during loading because of the interference of the filling mandrels with the movement of the upper layers of these bags. This interference often prevents the bags from opening completely requiring reduced loading operation speeds and occasionally requiring manual intervention.
In addition, known bags used in automated filling operations are problematic because of the substantial and nonuniform forces required to push the filled bag off the mandrel after loading. These forces, typically generated by the filling arm, involve breaking through a bridge portion of the bag material between the wicket opening (positioned on the mandrel) and the edge of the bag. Depending on the particular bag material being used, the force necessary to start the break (the initiation force) will vary substantially as the thickness and the width of the material to be fractured varies. In addition, the distance between the wicket opening and the filling edge of the bag (the width of the material to be fractured) may vary in production bags, due in part to registration or positioning problems which may occur when the wicket opening and other cuts are made. As a result, the forces required to fill the bag, initiate the break and to continue the break (the propagation force) may vary not only from bag to bag but within a given bag. These variations require different forces to be applied for different periods of time in order to fill the bag and ultimately push it off the mandrel at the appropriate time (i.e. after the bag is filled). The variations in forces can be extremely significant for certain types of bag material such as, for example, low density polyethylene which has a propagation force curve which increases with the stretching of the material until a fracture threshold is reached which occurs as the bag is pushed off the mandrel.
Yet another problem associated with wicketed bags of known construction is that the forces required to tear them from the filling mandrel often cause unwanted shards or fragments of bag material to tear and separate from the bag. These fragments are problematic in at least two ways. Loose fragments of polyethylene in a filled package are aesthetically unacceptable, and may even prove to be dangerous in, for example, food packaging applications where they can later be accidentally ingested. Moreover, these fragments often get caught in and jam the bag filling equipment causing significant down time.
The present invention represents a substantial improvement over known wicketed bags. The present invention utilizes a release path for facilitating bag opening and for disengaging the bag from the mandrel. The release path allows a lessened and substantially constant force to effect filling and release.